applied sciences Case Report Decision Support for Removing Fractured Endodontic Instruments: A Patient-Specific Approach Raphaël Richert 1,2,* , Jean-Christophe Farges 1,3, Cyril Villat 1,4,Sébastien Valette 1,5 , Philippe Boisse 2 and Maxime Ducret 1,3,* 1 Hospices Civils de Lyon, PAM Odontologie, 69007 Lyon, France; [email protected] (J.-C.F.); [email protected] (C.V.); [email protected] (S.V.) 2 Laboratoire de Mécanique des Contacts et Structures, UMR 5259 CNRS/INSA/Univ Lyon, 69100 Villeurbanne, France; [email protected] 3 Laboratoire de Biologie Tissulaire et Ingénierie Thérapeutique, UMR 5305 CNRS/UCBL, 69008 Lyon, France 4 Laboratoire des Multimatériaux et Interfaces, UMR CNRS 5615/UCBL, 69622 Villeurbanne, France 5 Centre de Recherche en Acquisition et Traitement de l’Image pour la Santé, UMR 5220 CNRS/INSERM U1206/INSA, 69100 Villeurbanne, France * Correspondence: [email protected] (R.R.); [email protected] (M.D.) Featured Application: Endodontics. Abstract: The instrumental fracture is a common endodontic complication that is treated by surgical or non-surgical removal approaches. However, no tool exists to help the clinician to choose between available strategies, and decision-making is mostly based on clinical judgment. Digital solutions, such as Finite Element Analysis (FEA) and Virtual Treatment Planning (VTP), were recently proposed in maxillofacial surgery. The aim of the current study is to present a digital tool to help decide between non-surgical and surgical strategies in a clinical situation of a fractured instrument. Five models Citation: Richert, R.; Farges, J.-C.; have been created: the initial state of the patient, two non-surgical removal strategies using a low or Villat, C.; Valette, S.; Boisse, P.; Ducret, high root canal enlargement, and two surgical removal strategies using a 3- or 6-mm apicoectomy. M. Decision Support for Removing Results of the VTP found a risk of perforation for the non-surgical strategies and sinus proximity Fractured Endodontic Instruments: A for surgical ones. FEA showed the lowest mechanical risk for the apicoectomy strategy. A 3-mm Patient-Specific Approach. Appl. Sci. apicoectomy approach was finally chosen and performed. In conclusion, this digital approach could 2021, 11, 2602. https://doi.org/ offer a promising decision support for instrument removal by planning the treatment and predicting 10.3390/app11062602 the mechanical impact of each strategy, but further investigations are required to confirm its relevance Academic Editor: Luca Testarelli in endodontic practice. Received: 6 February 2021 Keywords: finite element analysis; virtual treatment planning; endodontics; apicoectomy; Instrument Accepted: 5 March 2021 removal; decision-making Published: 15 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in 1. Introduction published maps and institutional affil- During cleaning and shaping of the root canal, troublesome incidents, such as the iations. fracture of the instrument, can occur. Many factors contribute to instrument fracture, and these have been associated with torsion stress or flexural fatigue [1]. The prevention of file separation has been widely investigated and is based on inspection of the file (notably of the winding of the flutes) or curvature management, which has led to more flexible Copyright: © 2021 by the authors. endodontic files [1]. However, the fracture of an endodontic instrument within the root Licensee MDPI, Basel, Switzerland. canal remains a common complication of endodontic treatments (0.25 to 7.41%), with This article is an open access article most fractures occurring in the apical third of the root [2,3]. This fracture can affect tooth distributed under the terms and prognosis, and several instrument removal strategies have been reported to complete the conditions of the Creative Commons endodontic treatment [1,4]. A non-surgical strategy was proposed using ultrasonic tips to Attribution (CC BY) license (https:// loosen the fractured instrument, but this procedure can lead to canal over-enlargement or creativecommons.org/licenses/by/ root perforation [5,6]. A surgical strategy was also reported to remove the instrument after 4.0/). Appl. Sci. 2021, 11, 2602. https://doi.org/10.3390/app11062602 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, 2602 2 of 9 performing an apicoectomy [7], but it induces a reduction of the crown-to-root ratio [8,9]. Both strategies thus impact mechanically the tooth and the success of the endodontic retreatment [10,11]. No tool exists, at the time of writing, to guide the clinician in choosing between these strategies, and decision-making is mostly based on clinical judgment instead of scientific evidence [3]. Furthermore, numerous different tools are available to deal with retained instruments, including mini forceps, broach and cotton, hypodermic surgical needles, wire loops, Masseran instruments, extractors, and ultrasonic tips [1,4]. In the face of the multitude of possible therapeutical choices, instrument removal is still considered highly technical and time-consuming because dental practitioners have difficulties planning the removal and its impact on tooth resistance. Digital approaches have been used for many years; for instance, virtual treatment planning (VTP) has been used to improve the reconstruction accuracy and outcome in the maxillofacial field [12,13], and patient-specific finite element analysis (FEA) has been used to provide better predictions on bone fracture than experienced clinicians in orthopedic practice [14]. In endodontics, FEA has been used to evaluate the influence of the instrument position and the resection length on the root stress distribution [15–17]. However, these studies use standard anatomic dimensions to create finite element (FE) models, and the success rate mainly depends on patient-specific parameters such as bone loss and canal anatomy [6,9,18]. A recent study proposed combining VTP and FEA for computer-aided decision-making, with the aim to predict the mechanical behavior of different maxillofacial surgeries and choose the most adapted solution for the patient [19]. Herein, we report a case of an endodontic instrument fracture and the application of a digital approach combining VTP and FEA to help decide between surgical and non-surgical strategies for its removal. 2. Case Report 2.1. Case Presentation A 26-year-old female patient was addressed to the department of endodontics of the Lyon University Hospital with a fractured instrument (FI) in the root canal of her right second maxillary premolar. The 8 mm-long instrument was fractured during an initial endodontic treatment of irreversible pulpitis one week previously. The patient reported no pain since the fracture occurred. Clinical examination of the premolar crown indicated the presence of four dental walls and a recent temporary restoration on the occlusal face. The tooth presented no cold response, no percussion or palpation tenderness, and physiological mobility. The intraoral periapical radiograph confirmed the transfixed position of the instrument, close to the sinus, and the absence of periapical radiolucency or local swelling of the sinus membrane (Figure1a). The patient’s tooth was scanned before any intervention to evaluate the instrument position using cone beam computed tomography (CBCT; Planmeca ProMax 3D, Helsinki, Finland) operating at 120 kV, 100 mAs, with a slice thickness of 0.75 mm. The data were recorded under the Digital Imaging and Communication in Medicine (DICOM) format and analyzed. Two non-surgical and surgical strategies emerged from the discussions of the healthcare team, but no consensus was defined on the treatment that could ensure the best outcome. A digital approach, combining VTP and FEA [19], was then implemented to visualize the planned treatment and predict the mechanical impact of the two removal strategies (Figure1). Appl. Sci. 2021, 11, x FORAppl. PEER Sci. REVIEW2021, 11, 2602 3 of 9 3 of 9 Figure 1.FigureThe process 1. The forprocess a patient-specific for a patient-specific biomechanical biomechanical analysis and analysis detailed stepsand detailed for virtual steps treatment for virtual planning and finite elementtreatment analysis: planning (a) radiograph and finite of element the initial analysis: situation ( presentinga) radiograph a fractured of the instrument,initial situation (b) cone presenting beam computed a tomographyfractured axial instrument, view with temporary (b) cone intracanalbeam computed medication, tomography (c) segmentation axial view based with on temp a growingorary regionintracanal algorithm, (d) transformationmedication, of ( thec) segmentation initial 3D image based to simulate on a growing a 3 mm apicoectomy, region algorithm, (e) analysis (d) transformation of the 3D simulated of the treatment, ini- and (f) meshingtial 3D of the image 3D transformed to simulate image a 3 mm to get apicoectomy, a finite element (e) modelanalysis and of application the 3D simulated of boundary treatment, conditions. and (f) meshing of the 3D transformed image to get a finite element model and application of boundary conditions. 2.2. Virtual Treatment Planning The different anatomical structures were segmented using DESK, an application suited 2.2. Virtual Treatmentfor medical Planning images [20]. The semi-automatic segmentation is based on the attribution of pixel labels, “seeds”, inside each anatomical structure and a growing region algorithm. The differentFour